1. Field of the Invention
Typically, a power plant of an automotive vehicle, including an engine and a transmission, is supported at a plurality of points by a power plant supporting structure. As is shown in FIG. 1, which illustrates a known power plant supporting structure, a power plant 21 is conventionally mounted at one point on a center beam or frame 101 of a front body structure by means such as a mount 105. The center frame 101 extends in a lengthwise direction and from the front to the back of the car body between a front cross member 102 and a suspension cross member 103, forming a part of a lower dash panel. Both of the cross members 102 and 103 extend transversely relative to the center frame 101.
2. Description of Related Art A power plant support structure such as that described above is known from, for example, Japanese Unexamined Utility Model No. 2-38,221. In such a support structure, during a front-end collision, the center beam 101 is deformed at its mid-portion, as shown by a chained line in FIG. 1. The cross member 102 and the mount 105, therefore, are forced rearward without deformation, and the support structure for the power plant 21 is unable to absorb an impact exerted on the power plant 21 during the front-end collision. Hence, the mount 105 collides against the power plant 21, as a result of a deformation of the center frame 101, and pushes the power plant 21 rearward. The amount of rearward displacement allowed for the mount 105 depends on what is called a "crush distance" or "crash-space," which is defined by a lengthwise direction D between the power plant 21 and the mount 105. Providing a small crash space in the power plant support structure is desirable in order to provide a compact engine room. However, providing such a small crash space also causes a large lengthwise movement of the power plant 21 during a front-end collision. The power plant, therefore, may possibly damage structural members of the passenger room and consequently injure occupants of the passenger room.
Another typical power plant support structure is disclosed by Japanese Unexamined Utility Model No. 60-40,836 and is shown in FIG. 2A. In this prior art power plant support structure, the power plant 21 is mounted at several points on a cross member 212 of a front body structure by mount assemblies 220. The mount assembly 220, to which the power plant 21 is secured through a bracket 206, comprises a mount member 222 and an adapter member 224. The adapter member 224 has legs 224a and 224b welded or otherwise secured to front and rear posts of walls 212a and 212b of the cross member 212. The mount member 222 is welded or otherwise secured to the adapter member 224. A steering rack 214 extends in the transverse direction over the cross member 212.
Such a mount assembly 220 is designed to make the legs 224a and 224b of the adapter member 224 short in length so as to increase the rigidity of the power plant support structure. In fact, as shown in FIG. 2B, upon, for instance, a front-end collision, the power plant 21 is forced or displaced rearward. Hence, the power plant 21 crashes against the steering rack 214 and, as a result, displaces the steering rack 214 rearward. Such a rearward displacement of the steering rack is, however, restricted by the rear wall 212b, projecting from the cross member 212. The amount of rearward displacement allowed for the steering rack 214 depends on the "crash-space," defined by a lengthwise direction D between the steering rack 214 and the rear wall 212b of the cross member 212. To adequately absorb an impact against the power plant when a front-end collision occurs, the power plant support structure must be improved to provide a sufficient a crash space.